Termite mound cover and abundance respond to herbivore-mediated biotic
changes in an African savanna
Abstract
Both termites and large mammalian herbivores (LMH) are savanna ecosystem
engineers that have profound impacts on ecosystem structure and
function. Both of these savanna engineers modulate many common and
shared dietary resources such as woody and herbaceous plant biomass, yet
few studies have addressed how they impact one another. In particular,
it is unclear how herbivores may influence the abundance of long-lived
termite mounds via changes in termite dietary resources such as woody
and herbaceous biomass. While it has long been assumed that abundance
and areal cover of termite mounds in the landscape remains relatively
stable, most data are observational, and few experiments have tested how
termite mound patterns may respond to biotic factors such as changes in
large herbivore communities. Here, we use a broad tree density gradient
and two landscape-scale experimental manipulations—the first a
multi-guild large herbivore exclosure experiment and the second a tree
removal experiment– to demonstrate that patterns in termite mound
abundance and cover are unexpectedly dynamic. Termite mound abundance,
but not areal cover not significantly, is positively associated with
experimentally controlled presence of cattle, but not wild
mesoherbivores (15-1000 kg) or megaherbivores (elephants and giraffes).
Herbaceous productivity and tree density, termite dietary resources that
significantly affected by different LMH treatments, are both positive
predictors of termite mound abundance. Experimental reductions of tree
densities are associated with lower abundances of termite mounds. These
results reveal a richly interacting web of relationships among multiple
savanna ecosystem engineers and suggest that termite mound abundance and
areal cover is intimately tied to herbivore-driven resource
availability.